java - JDBC : Operation not allowed after ResultSet closed

Question

这个问题已经有答案了:

Java JDBC MySQL exception: "Operation not allowed after ResultSet closed" (2 个回答)

Getting java.sql.SQLException: Operation not allowed after ResultSet closed (2 个回答)

已关闭 5 年前。

单击按钮时此代码显示此错误消息:

Operation not allowed after resultset closed

代码:

case 4:
                BufferedReader choosest=new BufferedReader(new InputStreamReader(System.in));
                System.out.print("enter your id");
                int idst=Integer.parseInt(choosest.readLine());
                String SQL = "SELECT * FROM student";
                ResultSet ps = stmt.executeQuery(SQL);
                while (ps.next()) {
                    int iddb = ps.getInt("id");
                if(idst==iddb) {
                    BufferedReader lessonuser = new BufferedReader(new InputStreamReader(System.in));
                    System.out.print("choose lesson ");
                    String lest =lessonuser .readLine();
                    String SQL1 = "SELECT * FROM lesson";
                    ResultSet qs = stmt.executeQuery(SQL1);
                    while (qs.next()) {
                        String ledb = ps.getString("namel");
                        if (lest == ledb) {
                            String insertTableSQL1 ="INSERT INTO chooselesson (id, lesson)  VALUES ("+idst+",'"+lest+"')";
                            stmt.executeUpdate(insertTableSQL1);
                            System.out.print("your unit sucssesfully add ");

                        }
                        }

                    }
                    }

Answer 1

当您进行另一个查询时，

ResultSet 将关闭。对于此代码，您可以首先收集ps的所有数据。然后迭代结果以执行其他查询。

我不得不说在循环中进行查询是很糟糕的性能操作。有很多方法可以避免这种情况。例如，您可以在一个查询中获取所有学生记录以及所有类(class)记录。然后使用lessonuser找出应插入chooselesson表中的记录，并以批处理模式运行insert SQL。